1. Field of the Invention
The present invention relates to an image processing system.
2. Description of the Prior Art
An apparatus which optically reads an image of a document with a photosensor, converts it to an electrical signal, processes the signal and prints it out has been known.
When characters comprising data are to be printed, it is necessary to read the document image while a transparent sheet bearing the data characters is overlayed on the document. This is a very inconvenient method.
On the other hand, it may be possible to electrically generate a character signal and combine it with a document image signal, but the resolving power for the inserted characters is lowered when the document image includes a half-tone image. Further, when the document image including a color image is reproduced, the inserted characters are sometimes not clearly reproduced depending on a background.
A binarizing processing method such as a dither method for reproducing gray levels of the document image has been known. It reproduces nxm gray levels with n x m pixels. As a result, the resolving power is lowered by a factor of n x m. Accordingly, the line image of characters included in the document may be unclear or combined characters may be unclear.
An apparatus which exposes a document image to an electrophotographic drum through an optical system and irradiates the drum with a laser beam modulated by a character signal to combine the document image and the character image has been known. However, this system is complex.
An apparatus which stores image data and other image data to be combined with the image data is also known. However, a long time is required to combine these types of data.
In a conventional color copying machine which uses a photosensitive medium or a laser beam color printer, a yellow or blue toner image is formed on the photosensitive medium, and transferred to a record paper. Then a magenta or green toner image is formed and transferred on the record paper. Next a cyan or red toner image is formed and transferred. And finally a black toner image is formed and transferred on the record paper. As a result, four color cycles are repeated even if a document includes only one color and hence the time loss is large.